1. Field of the Invention
This invention relates to video image recording and playback, and in particular, it relates to methods and apparatus for recording and playing back video images for a computer session.
2. Description of the Related Art
Video image recording is widely used in many practical applications. In many applications, the video images are either slow-changing (e.g. they often remain unchanged for extended period of time), or remain unchanged for large portions of the image (e.g. changes often occur only in small or scattered areas). One example is the recording and playing back of a computer session, i.e., the recording and playing back of the video images outputted by a computer to a user's monitor. In such an example, often large portions of the video image displayed on the monitor are unchanged. Another example of such an application is video surveillance, i.e. the recording and playing back of video images from a surveillance camera.
MPEG (including MPEG-1, MPEG-2, etc.) is a standard for widely used in digital video image compression and recording. MPEG uses interframe compression, i.e., compressing the current frame by using one or more earlier or later frames in a sequence, to reduce frame to frame redundancy. In interframe compression, certain frames, known as intra-frames or “I-frames”, are compressed without referencing to other frames. All blocks in the I-frame have the same timecode. Thus, MPEG's interframe compression tends to be inefficient for the above-discussed type of video signals.